1. Field of the Invention
This invention relates to drying kilns having improved insulation and more particularly to protection for the insulation to inhibit the deteriorating effects of the insulation being exposed to moisture.
2. Background of the Invention
Drying kilns are utilized to reduce the moisture content of lumber products that have been sawed from logs. The kilns generally are large buildings that have the capacity of handling thousands of board feet of lumber at a time. A conveying system, such as a fork lift truck, is provided to transport the lumber into and out of the kiln via an entryway. Most often the lumber is stacked in a layered configuration so that each lumber piece has each of its surfaces exposed to the surrounding air. Each layer of the lumber pieces is separated from each other by furring or spacer strips strategically placed along the lumber length so that warpage is minimized. In addition to the conveying system the kiln will have a heating system for heating air, a circulating system for circulating the heated air around and through the lumber and an exhaust system for exhausting the moisture laden air out of the kiln. The kiln is set up to circulate air through the stacked lumber with a continuous flow of heated dry air going into the kiln and warm moist air coming out of the kiln. The circulating of the heated dry air through the layers of lumber reduces the moisture content of the lumber.
Control of the temperature as well as minimizing the energy costs is important and consequently the insulation provided in the building walls and ceiling (roof) must be highly effective in preventing heat from being transferred through the walls.
Previously the insulation provided was not reliable over an extended period of time. The heavily moisture laden air would penetrate through the inner walls and moisture would condense to contaminate the insulation. The R value of the insulation dramatically dropped as the insulation absorbed moisture. Furthermore, most such inner walls are metal and the wet insulation abutting the metal (e.g. aluminum) walls accelerated corrosion. Typically, the drying kilns had to be refurbished on a frequent basis at a huge cost to the lumber mill.